26 May 2022 Thu 10.20 am

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As quantum technologies reach the Noisy Intermediate-Scale Quantum (NISQ) era, understanding the influence of disorder and noise on the dynamics of mesoscopic quantum systems becomes a problem of utmost importance. There are two possible causes of disorder: coherent disorder caused by structural flaws and incoherent noise caused by the presence of a thermal bath. This thesis investigates the dynamics of photons in the presence of both sources of disorder using the quantum photonics platform and provides novel methods to mitigate or utilize the error to improve photonic transport.

First, we propose coherent disorder-resistant waveguides, helical coupled-resonator optical waveguides (H-CROWs), by implementing topological transport in the bulk of a 1D waveguide that emulates at the boundary of a 2D quantum spin-Hall system. We show the robustness by showing enhancement of localization length and the purity conservation of propagating wavepackets. The preservation of temporal indistinguishability due to the suppression of group velocity fluctuations allows us to use the waveguide as a quantum channel to protect quantum resources, coherence and entanglement. In contrast to regular CROWs, which are highly sensitive to disorder, quantum state protection exhibits nearly perfect Hong–Ou–Mandel (HOM) dip visibility of identical single photons and inverse HOM dip of entangled photons.

Secondly, we suggest a novel method for cooling and enhancing heat transport in the presence of incoherent thermal noise by employing non-Kerr-type interaction. We study nonequilibrium quantum heat transport in the presence of a non-Kerr-type interaction governed by hyperparametric oscillation caused by two-photon hopping (TPH) between two cavities and a Kerr-type interaction such as cross-phase modulation (XPM). We predict that the system with TPH has a negative excitation mode and show that even though the interaction strength is low, the interaction allows the system to cool by inducing a ground-state transition as the particle number increases. We numerically demonstrate a transition of the heat current and show the enhancement of heat transport near the critical TPH interaction strength, whereas XPM does not exhibit any such transition.

Our findings could be helpful in a variety of aspects of quantum information processing and communication, such as preparing the ground state by cooling in an optical cavity and protecting quantum resources in optical links and delay lines. 

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